Personalized 21st Birthday Adult Sweatshirt. 21st Birthday Adult Sweatshirt - White has colorful bday balloons and slogan that says Party - 21 Rocks. Stay warm and stylish with this classic adult sweatshirt, perfect for everyday comfort. Crafted from soft, durable fabric, it features a relaxed fit for added coziness. Whether you’re lounging at home, running errands, or enjoying outdoor activities, this versatile sweatshirt is a wardrobe essential for any season.